Real-time volume rendering of 4-D image using 3-D texture mapping

4-dimensional (4-D) image is 3-dimensional (3-D) volume data that varies with time. It is used to express deforming or moving object in virtual surgery or 4-D ultrasound. It is difficult to render 4-D image by conventional ray-casting or shear-warp factorization methods because of their time-consuming rendering time or pre-processing stage whenever the volume data are changer. Even 3-D texture mapping is used, repeated volume loading is also time-consuming in 4-D image rendering. In this study, we propose a method to reduce data loading time using coherence between currently loaded volume and previously loaded volume in order to achieve real time rendering based on 3-D texture mapping. Volume data are divided into small bricks and each brick being loaded is tested for similarity to one which was already loaded in memory. If the brick passed the test, it is defined as 3-D texture by OpenGL functions. Later the texture slices of the brick are mapped into polygons and blended by OpenGL blending functions. All bricks undergo this test. Continuously deforming fifty volumes are rendered in interactive time with SGI ONYX. Real-time volume rendering based on 3-D texture mapping is currently available on PC.